1. Technical Field
The present disclosure relates to Differentiated Services and more specifically to automatic DSCP tracing for XoIP.
2. Introduction
The Internet Protocol (IP) was created without the ability to add priority to packets to allow latency-intolerant packets, such as voice packets, to be transmitted first during periods of congestion. As a result, Differentiated Services, or DiffServ, was created to allow management and prioritization of network traffic on modern IP networks. With DiffServ, network hardware marks packets on the network with a Differentiated Services Code Point (DSCP) mark, and other network hardware treats packets according to a corresponding level of service associated with the marks. Differentiated Services Code Point (DSCP) is a field in an IP packet that enables different levels of service to be assigned to network traffic. In particular, DSCP adds priority and offers different services to different types of packets. Routers in a DiffServ network can then pass high-priority packets during periods of high congestion, while delaying low-priority packets. Thus, DiffServ can, for example, provide low-latency to critical network traffic, such as voice or streaming media, while providing simple best-effort delivery to non-critical traffic, such as web browsing or file transfers.
A DiffServ network often includes a Service Level Agreement (SLA) Monitor that verifies service guarantees, validates network performance, and identifies network issues. Generally, an SLA Monitor server uses registered agents to trace the DSCP marking on the paths between the registered agents. A judicious selection of agents can be made to monitor the Customer Edge-Premise Edge (CE-PE) links of the network—where a substantial fraction of problems commonly arise—since even a large enterprise network may not have more than a few hundreds of such links.
However, QoS (Quality of Service) issues can also arise from the Local Area Network (LAN), and monitoring the LAN part of the network can be an extremely burdensome task, as typical monitoring approaches are difficult to scale to large networks. Furthermore, the registered agents perform DSCP and protection tests using User Datagram Protocol (UDP) traffic to specific ports. While this may be sufficient to detect some network performance issues, it greatly limits the registered agents' ability to detect issues with other types of traffic and ports, as network infrastructures often vary their treatment of different types of packets (e.g., UDP, TCP and ICMP) sent to different ports. For example, a UDP test to port 50012 may not reveal an issue with TCP traffic to port 80. Yet testing every combination of packets and ports is unfeasible. Consequently, the registered agents are often unable to detect a substantial amount of network issues.